<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
	</head>
	<body>
		<script>
			//Math.floor()向下取整
			alert(Math.floor(4.9));
			//Math.random()随机数
			alert(Math.random());
			//四位数取整
			alert(Math.floor(Math.random()*9000)+1000);
			
		</script>
	</body>
</html>
